New idea for current limiting for LowZ injectors

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ol boy
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New idea for current limiting for LowZ injectors

Post by ol boy »

I'm running 2 GM TBI's off of 87-93 GM truck with the 350 motor on a dual 4 barrel intake installed on a 289 SBFord. The injectors measure 1.2 ohms so I have installed 7 ohm, 50 watt resistors inline with each injector to limit current to 1.5 amps. My only issues is the opening time is now around 2.5ms and maybe longer.

The idea.. If it is possible to move the resistors to the grounding side of the injector instead of the power side then run a separate switching circuit from the top side of the resistor providing a brief 1ms timed pulse to open the injector. The main injector driver will then source all the current through the injector and resistor as normal. I would need to interrupt the signal from the MS to then turn on both outputs at the same time then turn off the opening pulse 1ms later and then the command pulse.

Thinking about it I maybe able to do this with the current PWM limiting output with the right settings....

Comments are welcomed..

Thanks Ryan
306 SBFord, Torquer II EFI intake, 60 lbs injectors, 8 LS2 coils, VS Racing 7668 turbo, 4R70W, MS3x fw1.4 w/built in trans controller.
racingmini_mtl
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Re: New idea for current limiting for LowZ injectors

Post by racingmini_mtl »

Do this with the standard PWM method or use external peak&hold drivers. Both of these are proven methods.

Jean
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Philip Lochner
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Re: New idea for current limiting for LowZ injectors

Post by Philip Lochner »

ol boy wrote:The idea.. If it is possible to move the resistors to the grounding side of the injector instead of the power side then run a separate switching circuit from the top side of the resistor providing a brief 1ms timed pulse to open the injector. The main injector driver will then source all the current through the injector and resistor as normal. I would need to interrupt the signal from the MS to then turn on both outputs at the same time then turn off the opening pulse 1ms later and then the command pulse.
Jaguar did exactly this on most of their V12 cars - ask me why I know.

The PWM function in MS2 is perfect for this application. I've got 3 V12's running like this with 6 loz injectors per output - no sweat. My MS ECUs only get luke warm.
Kind regards
Philip
'74 Jensen Interceptor 440ci (EFI'ed with MS2 and wasted spark + GM 4L60e GPIO controlled - both on Extra FW)
dontz125
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Re: New idea for current limiting for LowZ injectors

Post by dontz125 »

You wouldn't need to split or interrupt the signal with P&H. In your 'downstream' with the resistor, have a suitable N-channel MosFET and a 555 timer set up as a 1ms monostable (one-shot). When the MS starts the pulse, the timer activates the transistor bypassing the resistor. Once the 1ms is up, the resistor is back in the circuit; since this will be well into the 1A phase, this should help with heat dissipation in the P&H circuits.

This suggestion wouldn't work with PWM, since the timer would restart every time the signal was chopped!
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Matt Cramer
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Re: New idea for current limiting for LowZ injectors

Post by Matt Cramer »

The resistor with bypass is a crude peak and hold implementation. It may work but may take some dialing in of the peak time.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
billr
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Re: New idea for current limiting for LowZ injectors

Post by billr »

The P&H boards are so small, inexpensive, and reliable... why bother with anything else? I quickly decided not to "re-invent the wheel". It would be nice if something like the Cherry CS452/453 IC was still (easily) available new, but I couldn't find them.
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